Big bore 4stroke

[MyMistress86R]

Choose and discuss why...

If you were going for RELIABLE big bore in a 4 stroke motor...would you lean more towards bore or stroke to achieve your goals? Or a relatively even mix of both...

[Billy Golightly]

IF...I was going to a 4 stroke. It'd have to be the watercooled XR650 motor.

[cr480r]

I would lean towards big-bore over stroke... The reason being that the larger bore setups can usually fit and un-shroud larger valves... and a big bore is usually a much cheaper option... a stroker usually makes the rod/stroke ratio suck unless you get into long rods, custom pistons,balancing, longer timing chains, adjustable cam gears, cylinder spacers,etc..

[MyMistress86R]

OK Billy...why?

Keep the input coming guys...

[Billy Golightly]

Because you can get the equal horsepower out of those as a 450 class engine and not be a complete and utter time bomb like they are. Theres guys I know racing the nationals that have 55+ hp quads, and the motors are lasting about 3-4 hours of moto time. Practice hours. Thats bullshit. And if you leave it stock, it'll last forever. Theres a reason they ran those things in the Baja 1000 for ten years, and won just about every single one of them. The weight and size of the engine would suck, but I'd be able to live with it.

[Tri-Z 250]

The XR650 waterpumper is a load of a motor and tall. I agree totally w/Billy in the fact it's an excellent motor. On the bike I rode it was amazing how good the traction was even with a BEAT rear knobby. Power with control a seemingly endless topend. Yes, unless in the dunes or prarie, but fireroads or trails the term picket fence blur, worp speed Scotty comes on with the roll of the wrist. I did see someone posted up pics of a street legal 650XR trike on on this site.

I still like the overbore 2smoke...Cost, weight, size of head stock(stealthy bore). I guess my question to you is whats the build for? Drag, Trail, Track...MX, TT/Oval?

[The Goat]

Theres a reason they ran those things in the Baja 1000 for ten years, and won just about every single one of them. The weight and size of the engine would suck, but I'd be able to live with it.

big red pig....yeah but a big red pig that can break 110 mph with ease.

[RoscoW]

I'd also consider the Rotax motor in the Can-Am DS650, gearing is set up for quad trike use, dead stone reliable as well and E-start. Another large sized engine though.

Ross..